Lipid nutrition during early development of yellowtail flounder (Limanda ferruginea)

Copeman, Louise Audrey (2001) Lipid nutrition during early development of yellowtail flounder (Limanda ferruginea). Masters thesis, Memorial University of Newfoundland.

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Abstract

Yellowtail flounder (Limanda ferruginea) is a candidate species for cold-water aquaculture development in Atlantic Canada. However, mal-pigmentation and high larval mortality are still major obstacles to the successful culture of this species. Starvation due to inadequate nutrition is believed to be a major cause of this mortality. In particular, lipid nutrition has shown significant effects on the early development in a number of marine species. This study is the first examination of the dietary lipid requirements of yellowtail flounder larvae. -- Specifically, marine fish require the dietary polyunsaturated fatty acids docosahexaenoic acid (DHA, 22:6n-3), eicosapentaenoic acid (EPA, 20:5n-3) and arachidonic acid (AA, 20:4n-6) for normal growth and development. Consequently, in Chapter Two (Part A) an experiment was designed to study the role of dietary ratios of these fatty acids on the early growth, survival, lipid composition, and pigmentation of yellowtail flounder. Rotifers were enriched with experimental emulsions with high concentrations of DHA, DHA+EPA, or DHA+AA, or with a control (no DHA, EPA, or AA) emulsion. After four weeks, larvae fed the high DHA diet were significantly larger (9.7 ± 0.2 mm, p<0.05) and had higher survival (22.1 ± 0.4%), while larvae fed the control diet were significantly smaller (7.3 ± 0.2 mm, p<0.05) and showed lower survival (5.2 ± 1.9%). Larval lipid class and fatty acid profiles showed significant differences (p<0.05), with fatty acids reflecting dietary levels in the high PUFA diets. The incidence of mal-pigmentation was higher in the high DHA+AA diet (92%) than in all other treatments (<64%). It was concluded that yellowtail larvae require diets that are highly enriched with DHA while elevated dietary AA exerts negative effects on larval pigmentation. -- In Chapter Two (Part B) I examined the changes in growth and lipid composition that occurred when larvae of differing nutritional status were fed one diet of enriched Artemia. Significant changes in larval lipid class and fatty acid composition were observed after just two weeks of feeding on enriched Anemia. Control larvae showed a period of 'lipid recovery' while animals fed all other treatments showed a period of decreased lipid unsaturation. However, all larvae demonstrated a dramatic increase in size despite decreased dietary highly unsaturated fatty acids (HUFA). Therefore, it was concluded that high levels of HUFA may not be as essential during later larval development as during initial stages of first-feeding. -- In Chapter Three the lipid composition of mal-pigmented (MP) and normally pigmented (NP) newly settled yellowtail flounder were compared in order to elucidate a possible connection between lipids and pigmentation development. NP fish were found to be significantly larger than MP fish (p=0.04) at the time of 100% settlement. Higher relative amounts of triacylglycerols were found in NP fish (p=0.02) while MP fish had higher relative amounts of phospholipids (p=0.008). NP fish had higher relative amounts of DHA in the polar lipids of the body (p=0.03) and in the total lipids of the eye (p=0.04) than did MP juveniles. These data support previously proposed theories for the importance of DHA in pigmentation development.

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